It is described by Krishna how the soul becomes embodied according to his desire. So there are 8,400,000 types of bodies eternally existing. Not that the appearance of a new form in this world means that form has never existed previously. No, as conditions change on this earth planet, the living entities here desire to enjoy in a different way, so they take a different type of body. Even that body may be new here, it has always existed also somewhere else. So if a man qualifies for that body, he may be rewarded the body of superman, as he desires. So if someone wants such body, he must learn the process for acquiring it, that is Bhagavad-gita.
Letter to Upendra, 8 December, 1971